The present invention relates to the field of optical instruments for the examination of eyes. Such instruments are mainly used by medical practitioners and in clinics. The inventions relates mainly but not exclusively, to the examination of the human eye. It further relates mainly but also not exclusively, to the examination of the eye retina.
As prior art the following documents are mentioned: WO 90/03759 shows an optical instrument for examination of an eye using a light beam to scan a part of the retina and to produce images point by point according to a scanning method.
U.S. Pat. No. 4,838,679 shows a scanning optical instrument for the examination of an eye. Therein, a laser is used as light beam to scan a front part of the eye. A photo multiplier and an image memory serve to build up an image.
U.S. Pat. No. 4,715,703 shows an optical instrument for examination of an eye with a light source for illuminating the retina, an optical system for forming images of said retina and an electronic camera for producing data signals of said images. This instrument is not a scanning instrument.
Further, optical instruments using scanning systems are known in the market, such as the scanning laser ophthalmoscope of Rodenstock SLO and the laser scanning tomograph by Heidelberg Engineering.
Various software has been used in the past such as the NAVIS System database for optical instrument control and data recording.
Thus, with the prior art as known above, it is an object of the invention to provide a novel instrument and method for the examination of an eye.
It is another objective of the invention, to provide an optical instrument for the examination of an eye that has an improved flexibility.
It is still another objective to provide an optical instrument and method of the non-scanning type using an electronic camera to produce data signals of images formed in said camera with a light source to produce visible light patterns projected on the region of the eye.
Another objective of the invention is to provide a display as the light source in order to have flexibility in producing various patterns.
Various other objectives and advantages of the present invention will become apparent to those skilled in the art as a more detailed description is set forth below.
According to one aspect of the invention, it is proposed to use a LCD-display (liquid crystal display) for producing said light patterns. This relates to the optical instrument as well as to a method as described below.
An LCD-display offers very high resolution and is very flexible in view of the selection of the form, number, intensity as well as the movement of patterns and is available as a color display with a large multiplicity of colors for display.
According to a second aspect of the invention, the retina of the eye is examined and the optical instrument as defined herein comprises a computer control system for regulating the optical instrument, an input device to enable a patient to input a reaction during examination and an IR light source for illuminating the retina via the optical system. The electronic camera used is an IR camera which produces live image sequences. The optical instrument is also adapted to perform five different examination types, namely perimetry examinations, microperimetry examinations, fixation stability examinations, scotoma boundary detections, and psychophysical examinations.
During the perimetry and microperimetry examinations, the display produces fixation target patterns for fixation of the patient""s eye and light stimuli for stimulation of the patient""s eye. Light stimuli are selectable in position and intensity. The input device is used to detect a patient""s reaction as the stimuli is seen. By choosing various retinal positions, information concerning the sensitivity of the considered retinal region can be obtained, e.g. a complete sensitivity map.
During a fixation stability examination, eye fixation is performed by means of the above mentioned fixation target pattern. The optical instrument simultaneously performs live imaging of the retina, wherein the computer control system uses a correlation algorithm to detect movements of the retina and to collect fixation position movement data.
During a scotoma boundary detection, the above mentioned light stimuli are moved in their (projected) position on the retina towards a scotoma boundary region. The above mentioned input device is used to detect the patient""s reaction on whether a light stimulus, that has been seen before, vanishes or, vice versa, a light stimulus appears that has not been seen before. Thus, the scotoma boundary can be determined.
There also exists a variety of psychophysical examinations that have common test patterns for selection and projection onto the retina which is imaged in live image sequences simultaneously.
According to the second aspect of the invention, the optical instrument is adapted to offer all five examination types within one instrument and thus avoid the necessity of different instrument types and to shorten and ease a detailed examination session.
Preferably, the optical instrument according to the invention comprises an electronic camera for visible light as an additional or as the only electronic camera. The electronic camera for visible light thus provides xe2x80x9cnaturalxe2x80x9d images of the eye fundus obtained with visible light. However, in order to avoid a steady illumination of the eye in the visible spectrum, it is preferred to use a flashing light and thus to produce still images. Live sequences can be obtained by the IR system mentioned above.
Further it is preferred to use a mirror aperture in the optical system for reflecting illumination light from the IR light source via front lens into the eye. A central aperture of the mirror can first be used to transmit light from a front lens for an image of the eye region examined both for IR images and for visible light images. Further this aperture can be optically conjugated with the cornea in order to avoid a direct illumination of the cornea and for cornea reflex. The mirror aperture can also be used to couple invisible light from a flashing light via the front lens into the eye as with the IR illumination light.
The flashing light can be coupled into the optical path for the IR illumination light by means of a cold mirror which will reflect visible light and be transparent for IR light.
The visible light for the electronic camera can be branched-off the optical main path by a movable mirror which, preferably, is used to reflect light from the display to a calibration light sensor by means of its back side.
Further it is preferred that the computer control system of the optical instrument includes an autotracking system for automatically tracking fundus movements during the examination. Therein, a correlation algorithm is used for comparing image frames which can be a grey scale correlation algorithm. This algorithm returns the x and y shifts and the rotation of the currently acquired frame with respect to a reference frame. Preferably, the IR image frames of the live image sequences are used. By means of the correlation algorithm, image shifts between subsequent frames can be detected in order to control an adaptation system that automatically adapts the stimuli projection system to the eye fundus shifts. The x and y offsets of the fundus shifts and the value of the fundus rotation are then used to properly locate the stimulus on the LCD display in that position conjugated with the retinal area which the operator wants to stimulate.
The computer control system preferably selects a sub frame in a reference image which contains contrast structures for correlation calculations and the algorithm is performed only with regard to the sub frame. A preferred feature of the optical instrument according to the invention is that the auto tracking function can be used in each of the above mentioned examination types in order to improve speed, stability and quality of the examinations and images provided.
Finally, it is preferred that the computer control system be able to superpose graphical visualizations of examination results on still frame images, e.g. to produce still frame images with detected parts of a scotoma boundary or with sensitivity point measurements and the like.
The above explained embodiments of the invention and features refer both to the optical instrument and to the methods thereof.